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PLANT-BASED LOW-CARBOHYDRATE DIET AND BLOOD LIPIDS

  1. Top of page
  2. PLANT-BASED LOW-CARBOHYDRATE DIET AND BLOOD LIPIDS
  3. HIGH-GLYCEMIC-INDEX CARBOHYDRATES AND ENDOTHELIAL FUNCTION
  4. PROBIOTICS AND GLUCOSE REGULATION DURING PREGNANCY
  5. ANTIOXIDANT SUPPLEMENTS AND METABOLIC SYNDROME RISK

Jenkins DJ, Wong JM, Kendall CW, Esfahani A, Ng VW, Leong TC, Faulkner DA, Vidgen E, Greaves KA, Paul G, and Singer W. The effect of a plant-based low-carbohydrate (“Eco-Atkins”) diet on body weight and blood lipid concentrations in hyperlipidemic subjects. Arch Intern Med. 2009;169:1046–1054.

Diets with differing macronutrient profiles have received attention recently both in terms of optimal weight loss as well as in terms of impact on risk factors for cardiovascular disease. In particular, low-carbohydrate diets have come under scrutiny for possible negative effects on low-density cholesterol levels in individuals at risk for coronary heart disease. Traditional low-carbohydrate diets derive a significant proportion of nutrients from animal proteins and saturated fats, which is associated with increased risk for some cancers, heart disease, and other illnesses. For overweight individuals at risk for heart disease, a high-carbohydrate plant-based diet is typically recommended. However, recent work shows that diets with a higher protein, lower carbohydrate profile can be more beneficial in moderating blood lipids than the traditional high-carbohydrate diet. In the present study, Jenkins et al. compare the effects of two plant-based diets differing in carbohydrate content on body weight and blood lipids in overweight hyperlipidemic participants.

Forty-seven men and women were randomly assigned to either the high-carbohydrate control diet or the low-carbohydrate test diet. Metabolically controlled diets were provided to the participants for 4 weeks and were tailored to provide 60% of caloric requirements. The low-carbohydrate diet provided the minimum daily recommendation of 130 g/d carbohydrate and eliminated foods such as bread, rice, and potatoes. Plant-based proteins came from gluten, seitan, soy, and nuts. The control diet followed an ovo-lacto vegetarian low-fat plan. Primary outcome measures included weight lost over the 4 weeks and changes in blood lipids. After 4 weeks on the diets, both groups lost comparable amounts of weight (∼4.0 kg). For participants following the low-carbohydrate diet, greater reductions were seen in low-density lipoprotein cholesterol and total cholesterol relative to the high-carbohydrate diet, although both diets showed improvements in blood lipid measures. This study, while small-scale and short-term, provides evidence that a novel plant-based low-carbohydrate diet is beneficial in moderating blood lipids in hyperlipidemic individuals. While not directly addressed in the present paper, this type of diet may be particularly advantageous for individuals who must restrict carbohydrate intake but wish to minimize intake of animal proteins.

Comment: Drs. Tuttle and Milton emphasize that while the low-carbohydrate diet improved blood lipid profiles to a greater degree than the control diet, both diets were beneficial. They highlight the finding that both diets resulted in similar weight loss, indicating that caloric restriction rather than macronutrient composition is of primary importance in weight reduction. Finally, Drs. Tuttle and Milton urge long-term, larger-scale research on the “Eco-Atkins” diet prior to its recommendation for weight loss and cardiovascular risk reduction.

Comment: Tuttle KR and Milton JE. The “Eco-Atkins” diet: new twist on an old tale. Arch Intern Med. 2009;169:1027.

HIGH-GLYCEMIC-INDEX CARBOHYDRATES AND ENDOTHELIAL FUNCTION

  1. Top of page
  2. PLANT-BASED LOW-CARBOHYDRATE DIET AND BLOOD LIPIDS
  3. HIGH-GLYCEMIC-INDEX CARBOHYDRATES AND ENDOTHELIAL FUNCTION
  4. PROBIOTICS AND GLUCOSE REGULATION DURING PREGNANCY
  5. ANTIOXIDANT SUPPLEMENTS AND METABOLIC SYNDROME RISK

Lavi T, Karasik A, Koren-Morag N, Kanety H, Feinberg MS, and Shechter M. The acute effect of various glycemic index dietary carbohydrates on endothelial function in nondiabetic overweight and obese subjects. J Am Coll Cardiol. 2009;53:2283–2287.

Chronically impaired glucose control and poor blood glucose regulation are known risk factors for cardiovascular disease. In addition to the long-term consequences of hyperglycemia, acute, transient, post-meal hyperglycemia is also a cardiovascular risk factor in both diabetic and non-diabetic individuals. High intake of high-glycemic-index carbohydrates is associated with post-prandial hyperglycemia and increases risk for cardiovascular disease independent of other factors. Endothelial dysfunction is seen in individuals with hyperglycemia and diabetes, and is important in the development of atherosclerotic disease. The present study by Lavi et al. determined the impact of high- and low-glycemic-index carbohydrates on endothelial function in overweight and obese, but otherwise healthy, participants.

Participants (N = 56, 67.0% men) were given four different test meals on four separate test days, all participants received all test meals in a randomized order. After an overnight fast, participants given a test meal of water (placebo; GI = 0), glucose (50 ml; GI = 100), cornflakes (59 g; GI = 80), or high-fiber cereal (61 g; GI = 40). Endothelial function, as measured by endothelium-dependent flow-mediated dilation (FMD), was determined prior to and 120 min after the meal. C-reactive protein and lipoprotein levels were determined at baseline and 120 min post-meal. Blood glucose levels were measured at baseline, 30, 60, 90, and 120 min post-meal. Baseline levels of blood glucose and FMD were normal in all individuals. Blood glucose levels were significantly elevated at 30, 60, and 90 min following intake of glucose or cornflakes relative to water or the high-fiber cereal, and were still significantly higher following cornflakes at 120 min. Endothelial function was significantly reduced 120 min after intake of all meals, but was only significantly reduced following ingestion of either glucose or cornflakes. Alterations in endothelial function were not correlated with blood glucose levels or lipoprotein levels. These data show that short-term, single-meal intake of high-glycemic-index foods can alter endothelial function in individuals with normal baseline endothelial functioning and may not be related to alterations in blood glucose alone. The authors suggest that the link between high-glycemic-index foods and risk for cardiovascular disease may be, in part, determined by the effect of high GI foods on endothelial function.

PROBIOTICS AND GLUCOSE REGULATION DURING PREGNANCY

  1. Top of page
  2. PLANT-BASED LOW-CARBOHYDRATE DIET AND BLOOD LIPIDS
  3. HIGH-GLYCEMIC-INDEX CARBOHYDRATES AND ENDOTHELIAL FUNCTION
  4. PROBIOTICS AND GLUCOSE REGULATION DURING PREGNANCY
  5. ANTIOXIDANT SUPPLEMENTS AND METABOLIC SYNDROME RISK

Laitinen K, Poussa T, Isolauri E; Nutrition, Allergy, Mucosal Immunology and Intestinal Microbiota Group. Probiotics and dietary counselling contribute to glucose regulation during and after pregnancy: a randomised controlled trial. Br J Nutr. 2009;101:1679–1687.

Over the course of pregnancy, normal insulin and glucose tolerance shifts from normal towards insulin resistance. These changes direct metabolic fuels to the fetus and foster fetal growth and development. In some women, however, what is normally an adaptive process becomes pathological, and can lead to gestational diabetes. Impaired glucose handling can have negative long-term effects on the mother, placing her at risk for type 2 diabetes, as well as negative effects on the child, placing it at risk for metabolic abnormalities later in life. Dietary counseling to increase fiber and reduce fat and energy intake can be an effective means of maintaining normoglycemia in the mother. Metabolic abnormalities in glucose handling are associated with low-grade inflammation, and Laitinen et al. propose in this study that gut flora are important in mediating inflammatory response.

To establish whether probiotics would improve glucose handling, normoglycemic pregnant women (N = 256) were randomly assigned to one of three conditions – placebo, dietary counseling and placebo, or dietary counseling and probiotic supplement. The supplement contained Lactobacillus rhamnosus GG and Bifidobacterium lactis Bb12, intended to promote a microflora profile similar to that found in healthy breastfed infants. Dietary counseling was intended to modify food-intake patterns with particular attention to the quality of dietary fat. Participants were enrolled at less than 17 weeks' gestation, and study measurements were taken at ∼13 weeks, ∼23 weeks, and ∼33 weeks of gestation, and at 1, 6, and 12 months postpartum. The primary outcome measure was maternal glucose metabolism. Dietary counseling resulted in a reduction in saturated fat intake in both counseling groups relative to the control condition. In all groups, glucose concentrations decreased throughout pregnancy, and returned to normal levels in postpartum months. Better glucose tolerance was seen in the dietary counseling, probiotic intervention condition relative to the control condition. There was no probiotic without dietary counseling condition, so it is not possible to determine what the effects of probiotics alone on maternal glucose handling would be. The authors posit that probiotic supplementation alters gut microflora and thus modifies the intestinal immunological milieu, which improves maternal glucose handling. Use of a probiotic could therefore be useful as a prophylactic against metabolic disorders in pregnancy.

Comment: Dr. Cani in an accompanying commentary provides insight into the importance of gut flora in human health, including mucosal immunity, inflammatory bowel disease, and allergy. She underscores the importance of the Laitinen et al. study in that the study focuses on maternal metabolic homeostasis and is enthusiastic about the role of probiotics in the treatment or prevention of maternal metabolic disorders.

Comment: Cani PD. Gut microbiota and pregnancy, a matter of inner life. Br J Nutr. 2009;101:1579–1580.

ANTIOXIDANT SUPPLEMENTS AND METABOLIC SYNDROME RISK

  1. Top of page
  2. PLANT-BASED LOW-CARBOHYDRATE DIET AND BLOOD LIPIDS
  3. HIGH-GLYCEMIC-INDEX CARBOHYDRATES AND ENDOTHELIAL FUNCTION
  4. PROBIOTICS AND GLUCOSE REGULATION DURING PREGNANCY
  5. ANTIOXIDANT SUPPLEMENTS AND METABOLIC SYNDROME RISK

Czernichow S, Vergnaud AC, Galan P, Arnaud J, Favier A, Faure H, Huxley R, Hercberg S, and Ahluwalia N. Effects of long-term antioxidant supplementation and association of serum antioxidant concentrations with risk of metabolic syndrome in adults. Am J Clin Nutr. 2009 doi:10.3945/ajcn.2009.27635

Metabolic syndrome is a clustering of symptoms that include abdominal obesity, insulin resistance, high blood pressure, and hyperlipidemia. Metabolic syndrome is a recognized risk factor for the development of type 2 diabetes and cardiovascular disease and is characterized by an increase in reactive oxygen species and oxidative stress. Limited observations suggest an inverse relationship between components of metabolic syndrome and serum levels of antioxidants such as beta-carotene, vitamins E and C, selenium, and zinc. Few studies, however, have examined the relationship between antioxidant status and metabolic syndrome. Czernichow et al. report on a post hoc analysis of data from the Supplementation en Vitamines et Minéraux Antioxydants trial (SU.VI.MAX).

SU.VI.MAX is a long-term randomized controlled trial originally designed to assess the ability of antioxidant supplementation to reduce the incidence of cancer and cardiovascular disease. The trial ran from 1994 to 2002, and participants were randomly assigned to placebo or antioxidant supplementation and were followed for an average of 7.5 years. The antioxidant supplement was designed to provide nutritionally adequate doses of vitamin C (120 mg), vitamin E (30 mg), beta-carotene (6 mg), selenium (100 ug), and zinc (20 mg). Participants in SU.VI.MAX with available data on metabolic syndrome variables were identified (N = 5220) for the analysis on intervention effects. A subsample of participants with baseline antioxidant levels (n = 3336) was used to determine the relationship between serum antioxidant levels and risk for metabolic syndrome. The primary outcome measure was incident metabolic syndrome, as determined by waist circumference, fasting blood glucose, total cholesterol, and blood pressure. In the intervention group, blood levels of antioxidants increased significantly from baseline, and antioxidant levels were significantly higher in the treatment group relative to placebo. Over 7.5 years of follow-up, there were 263 cases of metabolic syndrome, but incidence of the syndrome did not vary with treatment condition, suggesting that intervention with antioxidant supplements does not affect the risk for developing metabolic syndrome. Baseline levels of vitamin C and beta-carotene were inversely related with the risk for metabolic syndrome. Baseline levels of zinc were positively associated with risk, and baseline levels of selenium and vitamin E were not associated with risk for developing metabolic syndrome.

When evaluating the current data it is important to consider that the original trial was intended to determine the impact of antioxidant supplements in risk for cardiovascular disease and cancer and the incidence of metabolic syndrome was relatively low (∼5%). The observation that supplementation with antioxidants did not alter the risk for metabolic syndrome is consistent with a growing number of studies that suggest such supplements do not confer appreciable benefits in generally well-nourished individuals. The authors argue that the increased risk for metabolic syndrome with higher baseline levels of zinc may be reflective of higher meat intake and possibly less healthy eating habits. The beneficial relationship between vitamin C and beta-carotene levels and reduced risk for metabolic syndrome suggest that intake of fruits, vegetables, and other plant foods contribute to a protective lifestyle in the prevention of metabolic syndrome.